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Issue 05/2016

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bioplasticsMAGAZINE_1605_

3D Printing PLA

3D Printing PLA homopolymers for 3D printing 3D printing materials Most 1 thermoplastics are suitable for use in the FDM process, each with their own advantages and disadvantages. The two most commonly used polymers for FDM processing today are PLA and ABS. Generally, ABS is preferred when strength, flexibility and higher temperature resistance is required in the final part. The smell when printing, however, together with the requirement of a heated bed, are considered to be the main disadvantages of ABS for FDM. With regard to PLA, the excellent aesthetics, colorability, seemingly sweet smell while printing, minimal warpage and biobased origin makes it the most popular choice for hobbyist 3D printers. A disadvantage of PLA can be its glass transition temperature of around 55 °C. Above the glass transition temperature, a polymer softens and loses its rigidity which can cause problems for those end-applications intended for higher temperature circumstances. Figure 2: The effect of PDLA on crystallization behavior Poly Lactic Acid A wide range of PLA polymers can be obtained by tuning its optical purity and molecular weight. At the heart of this technology, you find combinations of stereochemically pure PLLA and PDLA homopolymers, a type of PLA that is available from Corbion. These PLA homopolymers – and their associated compounds – boast improved properties and therefore open up new markets for bioplastic products, including consumer electronics, high heat packaging, automotive interiors, apparel and many more. They also bring new and improved properties to 3D printing when compared to standard 3D printing filaments currently on offer today. Nucleated Poly Lactic Acid compounds The performance of PLA can be tuned by the use of additives, like impact modifiers, fillers, plasticizers and nucleating agents. To close the properties gap between ABS and PLA, an impact modified compound (named Compound C) has been developed by Corbion based on PDLA nucleating technology. The use of an optically pure PLLA in combination with PDLA nucleating technology enhances the crystallization speed, whereby the crystallized end-product can withstand higher temperatures. Figure 2 shows the effectiveness of adding 5 % PDLA homopolymer to a PLLA homopolymer matrix. Crystallization was performed at 140 °C and monitored using a polarizing microscope with hot stage. The added impact modifier enables the PLA to improve its strength and flexibility. When crystallized, Compound C has similar haptics, aesthetics, heat resistance and mechanical properties to ABS. Figure 3 shows a 3D printed part based on Compound C. By: Martin Doornheim Application Development Corbion Gorinchem, The Netherlands 1 See separate box. FDM is still a registered trademark of Stratasys Fig. 1: PLA 3D printed part Fig. 3: PLA 3D printed part based on Compound C 44 bioplastics MAGAZINE [05/16] Vol. 11

3D Printing PLA homopolymers for 3D printing: a study A recent study by Corbion revealed that using a stereochemically pure PLLA showed advantages for 3D printed parts over standard PLA. In this study, the printing performance of ABS and standard PLA are compared with PLLA homopolymer and Compound C. Filaments were extruded and several models were printed. The models were carefully selected in order to best evaluate a number of different printing aspects: • Printing speed • Retraction behavior • Aesthetics (overhang, string formation, color) The models were printed using an Ultimaker 2 with a 0.4 mm nozzle, under the conditions listed in Table 1. Once printed, the final parts were placed in an oven at 80 °C for one hour to identify their heat resistance performance. Table 3: Printing window for PLLA Compound C Results The printing results are listed in Table 2. It was concluded that the two PLA homopolymer resins showed similar printing and retraction performance. The L175 resin (stereochemically pure PLLA homopolymer) showed exceptionally good clarity, meaning a lack of a yellow appearance. LX175 is a copolymer, Processing window test typically used for 3D printing. Surprising visual aesthetics 150 mm/s Bed conditions: Blue painters tape on bed, heated to 90°C 140 mm/s Unique visual characteristics have been discovered when 130 mm/s printing with PLA L175, 120 described mm/s as ‘glittering’ and ‘sparkly’ effects, as well as improved resolution. 110 mm/s 100 mm/s Compound C showed the broadest printing window, as 90 mm/s shown in Table 3. The horizontal axis describes the printer 80 mm/s head temperature and the vertical axis describes the printing 70 mm/s speed. 60 mm/s The retraction test 50 revealed mm/s that the PLLA compound achieved similar performance 40 mm/s to ABS. 30 mm/s 20 mm/s 10 mm/s Temperature (°C): 150 160 170 180 190 200 210 Processing window test Bed conditions: Blue painters tape on bed, heated to 90°C 150 mm/s 140 mm/s 130 mm/s 120 mm/s 110 mm/s 100 mm/s 90 mm/s 80 mm/s 70 mm/s 60 mm/s 50 mm/s 40 mm/s 30 mm/s 20 mm/s 10 mm/s Temperature (°C): 150 160 170 180 190 200 210 220 230 240 250 260 Legend: Underextrusion Good printing result Thermal degradation Irrelevant Legend: Table Underextrusion 1: printing conditions Good printing result Thermal degradation Irrelevant Printing head temperature (°C) PLA resins 210 ABS 240 Compound C 210 Printing bed temperature (°C) 60 90 60 Tape used yes/no no yes yes Table 2: Printing results (0: Similar to, -: worse than, +: better than the PLA benchmark) Test Standard PLA Corbion L175 Corbion LX175 Speed / temperature 0 0 0/+ - + Retraction 0 0 0 - - Aesthetic color 0 + 0/+ overhang 0 -/0 -/0 stringing 0 0/- 0 bioplastics MAGAZINE [05/16] Vol. 11 45

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